cappuccino/fetch: avoid ic request when waiting for ibus exception

The address that caused the bus error will stay on the
icache inputs until the exception is taken, asserting ic_req
then is requesting that faulty address again.
icache, dcache: allow accesses during refill

this enables accessing the caches while a refill is ongoing,
it also keeps track of the ongoing refill and acks accesses
to addresses that have been fetched into the current cacheline.